One of the most important things that affects the cost of a wireless base station is the design of the final, high power radio frequency (RF) amplifier used in, or with, the base station. Such amplifiers are themselves expensive. In addition, though, the RF output power capabilities of a particular amplifier have an impact on frame size, battery backup designs/costs, utility costs, air conditioning costs, etc.
Given the fact that RF power requirements have a direct impact on amplifier design and cost, it is important to control the maximum RF power demanded of an amplifier rather than oversizing the amplifier to handle surges in RF transmit power demand. In existing techniques, the maximum RF transmit power is controlled in a feedback loop independently of so-called call admission controls. This, unfortunately, can lead to a degradation in quality of service.
Historically, RF amplifiers used in base stations are selected for a given application based on a “steady state average” power rating and a “peak” power rating. As is known by those skilled in the art, the peak power rating applies to very short periods of time, usually measured in microseconds, to accommodate high peak to average ratios of spread spectrum signals, like Code Division Multiple Access (CDMA) signals. In between the times associated with steady-state and peak power ratings, other ratings or requirements are specified to establish a profile for the amplifier (e.g., a graph of power limit versus averaging time). For example, one or more points on the profile might be based on the ability of an amplifier to meet a spurious emission mask requirement at a power level higher than the steady state rating, for an averaging time measured in seconds. Other points with longer averaging times might be based on thermal limitations. Taken together, all of these considerations are used to form a maximum power versus averaging-time, amplifier power rating profile (profile). Rather than use oversized amplifiers, it would be advantageous to develop control techniques which place constraints on maximum RF power loads, measured with multiple integration time constants, so that the dynamic, RF load is consistent with the amplifier's profile. Such techniques should regulate an amplifier's output, to ensure that it does not exceed its transient and steady state power ratings, but should also do so in conjunction with call admission controls in order to preserve quality of service.